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f Assembly 
and many of them contain the Labrador feldspar. We do not, 
however, find the rock in place until we come into the north part 
of Schroon. The peculiar characters of this rock enable us to dis- 
tinguish its detached masses wherever they have been scattered. 
We observed many of them in Amsterdam, Montgomery county. 
Those we saw here contained more hornblende than usual. But 
boulders of this feldspathic rock, and containing the Labrador feld- 
spar, have been found in Orange county; also in St. Lawrence 
county, near Ogdensburgh. 
It is not intended to enter on the theoretical views, which facts of 
this kind and character are apt to elicit; but it is proper to say, 
this much, that it is supposed a current once swept over this 
country from north to south, and it is probable these boulders were 
borne along and left by it in the places we now find them. Those 
in St. Lawrence county, were by some means washed over the 
ridge into the basin of the St. Lawrence, or they might have drift- 
ed from Labrador on masses of ice ; the others were carried down 
the basin of the Hudson; and it will probably be established, that 
most of the boulders will be found in a south line from the county 
of Essex. None have been discovered east of the Taghkanick 
range, or west of Little-Falls. 
There is a peculiarity in this central nucleus of Essex which we 
feel bound to notice before we dismiss the subject. This whole ele- 
vated region is traversed by dykes of greenstone; these may be tra- 
ced uninterruptedly thirty or forty rods, and undoubtedly continue 
much farther. The discovery of these dykes in granite or sienite, 
though not entirely new, is one of interest in theoretical geology. 
Their occurrence is rare at least in this country. We first ob- 
served them in Elizabethtown, at Pleasant-Valley. Here they are 
not so well characterized as in some other places; for they are 
more like hornblende or pyroxene. Their width is not usually 
more than a foot, but in Keene they are from an inch to ten feet. 
The locality of greenstone dykes in the latter place, is at Long- 
Pond, a narrow sheet of water which lies in a cleft of two moun- 
tains. The sides of these mountains are-deeply furrowed by slides 
which have occurred from time to time. The widest is on the south 
side of the pond and about a hundred rods from its head. The pond, 
which is about thirty-five rods wide, is divided in two parts at this 
place by materials from the mountain. The strata laid bare by 
this means, exhibit these dykes, of which there are four running 
